Although designing and manufacturing ‘tall’ Tentec tensioners for these applications, is not usually a problem, in this case, the manway cover was located in the vertical plane where the minimum distance between the end of the stud bolt and a walled obstruction was just 100mm.

Hydraulic bolt tensioners for this application would normally comprise a number of ringed segments, each containing an equal amount of load chambers. The chambers are linked internally in each segment so that hydraulic pressure introduced into a single port via hose pressurises each chamber simultaneously. Multiple hoses from the hydraulic power pack mean that all segments are pressurised at the same time and so tensioning all stud bolts simultaneously and with equal force.

However, due to the orientation of the cover and the access limitation, it was apparent that assembly of a segmented ring would be difficult. The engineers at Atlas Copco Bolt Tightening Solutions devised an unconventional solution - the tensioner was designed as a complete ring instead of individual segments.

In the final design, the tensioner was made of 3 rings, each less than 100mm tall and individually lowered by hoist, through the 100mm space and onto the manway cover. All 20 chambers were internally linked and although, theoretically, may be pressurised via a single hose from the power pack, the ring contained 5 ports, equally spaced radially so that fluid supply was evenly and efficiently supplied to all chambers.

Speaking about this innovative solution, Dave Evans, Engineering Manager commented: “We have been dealing with the nuclear industry for many years and have never encountered a similar problem. However, our engineers have plenty of experience designing customised solutions throughout the range of industries in which we work and applied their extensive bolt tensioning knowledge to design this innovative and unique MST.”